I just purchased a MacBook Air with OSX v10.8.4. When I edit the modifier keys (I want to change Caps Lock to Ctrl), it works for a while, but then reverts back to defaults some time later. I'm making the changes here

System Preferences -> Keyboard -> Modifier Keys...

I just tested making the change, closing the lid, then opening it. The change stuck past that. So I'm not exactly sure when the settings revert, but they do eventually revert back to the defaults.

I have been experiencing the same problem, but in OSX 10.9.4. Namely, in System Preferences I remap Caps Lock to Ctrl, and it reverts itself back to Caps Lock after a day or two for no discernable reason.

To solve this you can use Seil to remap your Caps Lock key. Additionally, you can use Karabiner for a huge range of other keyboard settings.